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The term nonionizing radiation refers to several forms of electromagnetic radiation of wavelengths longer than those of ionizing radiation. As wavelength lengthens, the energy value of electromagnetic radiation decreases, and all nonionizing forms of radiation have less energy than cosmic, gamma, and x-radiation. In order of increasing wavelength, nonionizing radiation includes ultraviolet (UV) radiation, visible light, infrared radiation, microwave radiation, and radiofrequency radiation. The latter two are often treated as a single category. The energy, frequency, and wavelength range for electromagnetic forces are shown in Table 36-1. All forms of electromagnetic radiation have the same velocity of 3 × 1010 cm/s in a vacuum.


Radiation is emitted continuously from the sun over a wide range from 290 nm in the ultraviolet range to more than 2000 nm in the infrared range with a maximum intensity at about 480 nm in the visible range. The radiation from the sun is modified as it passes through the earth's atmosphere. Ozone, which is found in the upper atmosphere, absorbs the highest energy ultraviolet radiation. Infrared radiation is absorbed by water vapor, and other wavelengths are altered by passage through smoke, dust, and gas molecules.

All objects above absolute zero temperature emit radiation, much of it as infrared radiation. At low temperatures, only long wavelength radiation is emitted, but as the temperature of the objects increases, shorter wavelength radiation is emitted. Heated metal gives off a red glow; if heating continues, the metal becomes “white hot” as energy throughout the whole visible spectrum is given off. Heated gases may give off wavelengths in the ultraviolet, visible, or infrared regions. Ultraviolet radiation is given off with the use of extremely high-temperature welding equipment such as carbon or electric arcs.

The biological effect of radiation exposure depends on the type and duration of exposure and on the amount of absorption by the organism. The carcinogenic and other effects of ionizing radiation are discussed in Chapter 36.


The sun is the major source of ultraviolet radiation although there are artificial sources such as electric arc lights, welding arcs, plasma jets, and special ...

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